1. Field of the Invention
The invention relates to the non-contact testing of electrical characteristics of electronic components, such as the insulation between conductors, the electrical continuity of conductors, resistance, and even capacity and inductance. The testing is non-contact in the sense that an injection or an extraction of electrons in the conductors to be tested is obtained by an electron tearing effect under the effect of an electromagnetic beam (in principle a beam of ultraviolet rays) having a photon energy greater than the energy for extracting an electron from the conductor.
2. Brief Description of the Related Art
Non-contact test devices are principally intended for checking the electrical interconnections in interconnection supports such as printed circuits or, above all, integrated circuit support substrates (known as “chip-carriers”) having a very large number of output terminals. With the reduction of the dimensions of integrated circuits and the increase in the density of the connections, electrical testing becomes difficult and can no longer be done by direct contact between test points and the conductive areas to be tested.
Typically, in order to mount an integrated circuit on a printed circuit, there is interposed an interconnection substrate (or “chip-carrier”) having hundreds of very dense contact areas on the side which receives an integrated circuit chip which has a very large number of contacts, and having an often smaller number of contact areas on the rear, on the side which will be soldered on the printed circuit. As much as it is possible to apply test points on the rear side, in the form of what is known as a “bed of nails”, that is to say an addressable matrix of contact points, because the contact density is lower, it is however almost impossible to do so on the side which carries the chip. Non-contact test systems have therefore been developed to allow the testing of the interconnection substrate from the side which carries the chip. The testing can moreover be carried out in a mixed manner with test points (or another access mode using direct contact) on the less dense rear face and a non-contact test on the more dense front face.
There have already been proposed non-contact test devices capable of either extracting electrons from a conductor to be tested, or of injecting electrons into that conductor, or finally of carrying out an extraction operation and an injection operation simultaneously on two portions of conductor in order to test the insulation, continuity, or resistance between these two portions. The patent application WO 01/38892 and the patent U.S. Pat. No. 4,573,008 describe such devices.